Process for the production of pure aqueous potassium as sodium hexacyanoferrate (iii) solution

ABSTRACT

PURE AQUEOUS SOLUTION OF POTASSIUM HEXACYANOFERRATE (III), SODIUM HEXACYANOFERRATE (III) AND SODIUM POTASSIUM HEXACYANOFERRATE (III) ARE PREPARED BY OXIDATION OF THE CORRESPONDING HEXACYANOFERRATE (II) SOLUTIONS WITH ACIDS CONTAINING THE GROUP (FE(CN)6) AND AN OXIDIZING AGENT HAVING AN OXIDATION POTENTIAL GREATER THAN +0.46 VOLT.

United States Patent Office 3,707,449 Patented Dec. 26, 1972 PROCESS FORTHE PRODUCTION F PURE AQUE- OUS POTASSIUM AS SODIUM HEXACYANOFER- RATE(III) SOLUTIUN Helmut Reinhardt, Weiss, and Karl Trehinger and GottfriedKallrath, Wesseling, Germany, assignors to Deutsche GoldundSilber-Scheideanstalt vormals Roessler, Frankfurt am Main, Germany NoDrawing. Continuation-impart of application Ser. No. 129,173, Mar. 29,1971. This application May 17, 1971, Ser. No. 144,289 Claims priority,application Germany, Apr. 9, 1970,

P 20 16 848.3; May 3, 1971, P 21 21 647.7 Int. Cl. C01c 3/12 US. Cl.20491 7 Claims ABSTRACT OF THE DISCLOSURE Pure aqueous solution ofpotassium hexacyanoferrate (III), sodium hexacyanoferrate (III) andsodium potassium hexacyanoferrate (III) are prepared by oxidation of thecorresponding hexacyanoferrate (II) solutions with acids containing thegroup [Fe(CN) and an oxidizing agent having an oxidation potentialgreater than +0.46 volt.

The present application is a continuation-in-part of application Ser.No. 129,173, filed Mar. 29, 1971.

It is known to produce potassium hexacyanoferrate (III) solutions by theelectrolytic oxidation of potassium hexacyanoferrate (II) solutions orby oxidation with known oxidizing agents such as chlorine, chloride oflime (bleaching powder), lead dioxide, bismuth pentoxide, calciumplumbate or persulfate (Ullmann, Encyclopedia der Technischen Chemie,vol. 5, 1954, page 659). It is also known to produce potassiumhexacyanoferrate (III) by oxidation with air under pressure (SchroterGerman Pat. 502,883).

Common to all of these processes is the fact that a part of the addedpotassium ions are lost as by-products. Besides the reaction solutionbecomes alkaline if the potassium hydroxide formed is not neutralized bythe addition of foreign ion containing acids. Only in this way is thereverse reaction to form potassium hexacyanoferrate (II) avoided.

It has now been found that pure aqueous potassium hexacyanoferrate (III)solutions can be produced in neutral medium with use of the entireamount of potassium ion present if aqueous solutions of potassiumhexacyanoferrate (II) are reacted with an oxidizing agent whoseoxidation potential is greater than +0.46 volt in the presence of anacid containing the group [Fe(CN) i.e. H.,[Fe(CN) or H [Fe(CN) In placeof potassium hexacyanoferrate (III) there can be produced in the sameway with equally good yields sodium hexacyanoferrate (III) and sodiumpotassium hexacyanoferrate (III), Na K [Fe(CN) by employing as thestarting material aqueous solutions of sodium hexacyanoferrate (II) anda mixture of sodium hexacyanoferrate (II) and potassium hexacyanoferrate(II).

As oxidizing agents there can be used water soluble permanganates, e.g.,sodium permanganate, potassium permanganates and ammonium permanganate,water soluble manganates, e.g. potassium manganate and sodium mtnganate,water soluble dichromates, e.g. ammonium dichromate, potassiumdichromate and sodium dichromate, water soluble cerium (IV) salts, e.g.ceric sulfate, water soluble bromates, e.g. sodium bromate and potassiumbromate, as well as lead dioxide, nitrosyl gases, oxygen e.g. as pureoxygen or as air and hydrogen peroxide. Electrolytic oxidation is alsouseful.

Especially suitable as oxidizing agents in which after the reaction theonly by-product present is Water are oxygen and hydrogen peroxide.Likewise the electrolytic oxidation is preferred. In the latter case theonly byproduct in addition to water is the acid employed. Mostespecially suitable is hydrogen peroxide.

'Ihe reactants, i.e. the potassium hexacyanoferrate (II) (or sodiumhexacyanoferrate (II) or mixtures of sodium and potassiumhexacyanoferrate (II)), the oxygen providing substance and the acid areadded in equivalent amounts. This is also true for the anodic oxidation.

Hydrogen peroxide can be added as an aqueous solution of knownconcentration, e.g. 3 to weight percent solution, preferably as a 10 to50% solution,

The potassium hexacyanoferrate II (or sodium hexacyanoferrate (II) ormixture of sodium hexacyanoferrate (II) and potassium hexacyanoferrate(11)) generally is present as a 10-45 weight percent aqueous solution.

As acids which contain a [Fe(CN) group there can be employedhydroferrocyanic acid, H [Fe(CN) and hydroferricyanic acid, H [Fe(ON)They can be prepared in known manner by reaction of their barium saltswith sulfuric acid or their alkali salts, e.g. sodium or potassium saltswith mineral acids such as hydrochloric acid, sulfuric acid, hydrobromicacid, phosphoric acid, etc. According to a further proposal according tothe invention an especially pure aqueous hydroferrocyanic acid orhydroferricyanic acid is produced by reaction of an aqueous solution ofthe corresponding alkali metal salts, e.g. the sodium and potassiumsalts, the potasium salt being especially preferred, on acidic exchangeresins. The thus obtained hydroferrocyanic acid or hydroferricyanic acidis salt free and free of foreign acids. As ion exchangers there can beused strongly acid cation exchangers, particularly sulfonated cationexchange resins such as those set forth in DAlelio Pat. 2,366,007 e.g.insoluble sulfonated styrene resins such as sulfonated styrene-divinylbenzene resin (e.g. Dowex 50 and Amberlite IR-120), as Well assulfonated phenol-formaldehyde resins.

If a solution of potassium hexacyanoferrate (II) is used for thecontinuous production of potassium hexacyanoferrate (III) (or a solutionof sodium hexacyanoferrate (II) for the production of sodiumhexacyanoferrate (III)) which is obtained by the reaction of itspotassium salt (or sodium salt) with an ion exchange resin there occursno loss of potassium ion (or sodium ion) during the entire cyclicprocess including the obtaining of the potassium hexacyanoferrate (II)(or sodium hexacyanoferrate (11)) charged, since this is recovered fromthe ion exchanger by acid rinsing and is reduced to the step ofproducing the potassium hexacyanoferrate (II) (or sodiumhexacyanoferrate (11)).

The process of the invention is carried out in known manner in mixingvessels in which there are provided propellers, turbines or discstirrers for adequate intermixing, as well as in rotary mixers. Thetemperature of the reaction is not critical, e.g., it can be 40 to C.

3 The process is also normally carried out at atmospheric pressure andthere is no need to use pressure equipment.

If oxidizing agents are added which provide no byproducts besides water,it is possible to recover potassium hexacyanoferrate (III) (or sodiumhexacyanoferrate (III) (or sodium potassium hexacyanoferrate III (as asolid from the resulting pure solution in simple manner by directcrystallization or spray drying. In the other cases it is necessary towork up the solutions by customary methods.

The technical advantages of the process of the invention include thefact that the oxidation of the potassium hexacyanoferrate (II) (orsodium hexacyanoferrate (11)) occurs in neutral or acid medium, e.g., pHof 1 to 7 and thereby is avoided a back reaction through hydroxyl ionsformed in the reaction solution, i.e., the hexacyanoferric acidneutralizes the hydroxide formed. Furthermore by the presence of an acidof the same ion acid, the potassium ion (sodium ion) added is reactedquantitatively in the end product and unlike previous procedures is notlost in part as by-product. Besides no foreign ions are brought into thereaction mixture through the acid which can later cause problems in theworking up.

Unless otherwise indicated all parts and percentages are by weight.

The invention will be explained further in connection with the examples.

EXAMPLE 1 2.3 m. (cubic meters) of an aqueous potassium hexacyanoferrate(II) solution containing 210 grams of K [Fe(CN) -3H O per liter weremixed in a container provided with a stirrer with 0.76 m. of an aqueoussolution of H [Fe(CN) containing 110 grams of per liter. The mixture waswarmed to 60 C. and inside 10 minutes was oxidized with 258 liters of a10% aqueous hydrogen peroxide solution. During the oxidation thetemperature rose to 76 C.

There was formed 3.3 m. of an aqueous potassium hexacyanoferrate (III)solution having a content of about 150 grams of K [Fe (CN per liter.

EXAMPLE 2 837 cm. (cubic centimeters) of an aqueous solution of H[Fe(CN) having a hexacyanoferrate (II) content of 0.6 mole per liter wasplaced in a 4 liter flask and treated with 634 grams of crystalline K[Fe(CN) -3H O. This mixture was heated to 60 C. a clear solution wasobtained. Inside 10 minutes there were introduced 111 grams of perhydrol(an aqueous solution of H containing about 32 weight percent of hydrogenperoxide) diluted with water to 500 cm. The reaction temperature rose toabout 80 C.

There was obtained a K [Fe(CN) solution with a content of 345 grams of K[Fe(CN) per liter. The yield was quantitative.

EXAMPLE 3 Aqueous solutions of K [Fe (CN 3H O and H [Fe (CN were mixedin the proportions set [forth in Example 1. This mixture wassimultaneously introduced into a reactor with the necessary amount of anaqueous H 0 solution (having an H 0 concentration of The temperature inthe reactor was held at 60 C. The residence time of the reaction mixturein the reactor on the average was 10 minutes. By continuous removal ofthe K [Fe(CN) solution prepared the reaction volume was maintainedconstant.

EXAMPLE 4 A customary cation exchange resin (sulfonated styrene-divinylbenzene resin) was converted to the hydrogen form in known manner andsubsequently washed free of electrolyte.

565 cm. of the hydrogen form of the ion exchange resin were charged witha solution of K [Fe(CN) solu tion having a content of K [Fe(CN) 3H O of212 grams per liter with a speed of passage of 1 liter of solution perhour.

There was obtained an aqueous solution of with a content of grams of H[Fe(CN) per liter of solution.

EXAMPLE 5 One liter of a hot (80 C.) aqueous sodium hexacyanoferrate(II) solution, containing 395 grams of One liter of an aqueous solution,containing 84 grams of sodium hexacyanoferrate (II) (Na [Fe(CN) ]-10H Oand 147 g. of K [Fe(CN) ]-3H O, was mixed with 324 cm. of an aqueoussolution of H [Fe(CN) containing 116 g. of the acid per liter and 42 g.of a 32 weight percent of aqueous hydrogen peroxide were mixed andheated to 60 C. The reaction temperature rose to about 73 C. during theoxidation. There was obtained 1.4 liter of a K Na[Fe(CN) solution with acontent of g. of.

K Na[Fe(CN) per liter. The yield was quantitative.

The solutions of sodium and potassium hexacyanoferrate (III) preparedaccording to the present invention can be employed as starting materialsto prepare other complex cyanides in known manner.

What is claimed is:

1. In a process for the production of pure aqueous alkali metalhexacyanoferrate (II) solutions selected from the group consisting ofpotassium hexacyanoferrate (III), sodium hexacyanoferrate (III) andsodium potassium hexacyanoferrate (III) by oxidation of thecorresponding alkali metal hexacyanoferrate (11) solution theimprovement comprising carrying out the oxidation with an oxidizingagent having an oxidation potential greater than +0.46 volt with an acidcontaining the [Fe(CN) group selected from the group consisting of H[Fe(CN) and 3E )6].

2. A process according to claim 1 wherein the oxidation is carried outwith an oxidizing agent selected from the group consisting of oxygen,air and hydrogen peroxide.

3. A process according to laim 2 wherein the oxidizing agent is aqueoushydrogen peroxide of 10 to 50% concentration.

4. A process according to claim 1 wherein the oxida tion is carried outelectrolytically.

5. A process according to claim 1 wherein the alkali metalhexacyanoferrate (III) and (II) are potassium hexacyanoferrate (III) and(II).

6. In a process for the production of pure aqueous aqueous alkali metalhexacyanoferrate (III) solutions selected from the group consisting ofpotassium hexacyanoferrate (III), sodium hexacyanoferrate (III) andsodium potassium hexacyanoferrate (III) by oxidation of thecorresponding alkali metal hexacyanoferrate (II) solutionelectrolytically or with hydrogen peroxide, oxygen or air 5 6 theimprovement comprising neutralizing the hydroxide FOREIGN PATENTS formedwith H [Fe(CN) or H [Fe(CN) 7. A process according to claim 6 whereinthe alkali 55 2/1930 Great Britain 2Q4 91 metal hexacyanoferrate (III)and (II) are potassium hexacyanoferrate (III) and (II). 5 497584 12/1919France References Cited F. C. EDMUNDSON, Primary Examiner UNITED STATESPATENTS 1,589,041 6/1926 Barsky 2377 l0 1,872,929 8/1932 Glnud et a1.2377 2377 2,261,672 11/1941 Barnes et a1. 2377

